Cathodic protection of metal in vapor space



o. E. ANDRUS 2,744,863

CATHODIC PROTECTION OF METAL IN VAPOR SPACE May 8, 1956 Filed Oct. 251951 INVENToR. Orrm E Andrus BY @mq/WAV ATTORNEYS.

nited States Patent CATIv-GDIC'PROTECTIGNOF METAL 1N VAPQR'.f

SPACE Orrin E. Andrns, Milwaukee, Wis;,'assignor to A. O. SmithCorporation, Milwaukee, Wis.,a corporation of New York-Applicationctoberf25, 1951, Serial No. 253,060 4 Claims. .(Cl. 21M- 196)electrolyteor the surface was in contact with a substance,

such as earth or soil, bearing an electrolyte. Surfaces in contact withvapors have not been protected cathodically in a commercial manner.

The .'present invention is directed to ameans o f cathodicallyprotecting metal-surfaces which are in contact with a vaporousmediumfthatis capable of conducting an electric current whencondensed.To carryout the invention, the metal surface to be protected is'initially coated withan absorbent material such as felt, asbestosfiber, or the like.I An expendable perforated metal liner isapplied* tothe coated 'surface' with the `intermediate labsorbent coating Vservingto separate-one metal surface from Thecorrosive-,condensate in theVapor-region-passes between -the linen-plates and is absorbed -inl theinsulating" coatingjto-formv an electrolyte therein;A

Corrosion of the expendable liner maythen be pro moted--byeitherapplying a--lowl-voltage current -tothe unit withthe liner-'beingmadeY the anode and the surface to be protected-,the cathode,- orsecondly, by employing a metal which-isanodic tothe -surfacef-to-beprotected as the liner andproviding-electrical-contact-between-saidsurface-andthe linen-such asbya number-of4 retaining studs-- One object of the present-invention is'tovprovide an -Y effective means of-cathodicallyprotectinga'metal-surface in contact with a Vaporous--medium which-isIcapable ofv conducting arr electrical current when condensed.

Anotherobject of the invention is-A to provide an elec-- tzrolyte-inrthe `vapor-or sprayfregiont. which establishes` electrical-1contactibetweenthe -1netal1surface-Ltol be protected-4 and :a second-expendablemetal, surface'.-

Still another objectissto provide .a simple .and inerty pensive:methQd-Jof protecting;metalisurfaces.exposed-xto- 'r1corrosive?condensatelirr. the vaporIV region-pwherebyr ythe condeuatefisabsorbed .in an insulating material and functions as, an electrolyte.

In the drawingsgtx,

taininghjthe present invention;

Figfllis an enlarged fragmentary sectional-.view showing the attachmentof the invention to the tank surfaces;

FigJ-S-is a second embodiment of-the invention showing asideelevationpartially-insection-of a tank containfing theinventiongiand w1' Fi g.1.'=4 :is an; enlarged `fragmentaryi sectional`View showa ing .the :.a-.ttacli.menty 1of` the embodiment, l.of Figrto;the

taule-surface..

'ice

Referring to the drawings, there is.shown.in.Figures. 1... and 2 anembodiment -of the present invention. as applied. to a .tank..1.Whichis-.to be protected cathodically. from corrosive vapors..

Tank 1 is Vadapted to contain Water or any other liquidv 2 which willevaporate andsaturate the .air abovel the liquid level with vaporwhichin itself is capabley of con,

ducting an electrical current when condensed. Tank .1,

comprises a generally cylindrical.body section 3 havingv the upper endthereof enclosed by a roof member 4 and the bottom thereof enclosed by afloor 5.

Roof member 4 and floorl 5 are secured. to body sectiony 3 by welding toprovide an integralleak-tight container. Tank 1 is constructed. of'steel or any high-strength Imetal and is designed with a..thicl 'ness towithstand the force.

ofthe internal pressure exerted by the contained water or liquid.

As shownin the first embodiment of the invention the inner surface oftank 1.`is.covered with a protective'coating 6,N such as glass, plastic,enamel or the like. Coating 6, as applied, may contain"v minuteimperfections,

cracks or discontinuities. The-vapor. contained. within tank. 1 maycondense at the tank surface and penetrate into.. these imperfections`causing..intensified corrosion of the tank at the p ointof penetration.

To protect the tank from this'corrosion, a porous .ab-L sorbentinsulating material-7,1such as felt,.asbestos ber; f

glass wool or the like is applied to the 'inner rsurfaces of tank 1'which are to be exposed'to the condensed' vapor.V y

A metal linerV 8 is disposed against theinsulatingmate.- rial 7 to connethe same, and the materia1;7 serves kto separate .and insulatethe metaltank. 1 from the metal Liner -8 may consist-'of largeor small areasv ofscrap steel-or other metal,v `or it may consist of sections ofperforated metal'plate,--'as shown-in the drawings. Since Y' the liner-8is not intended togivey physical'strengthitothe -tank or to prevent lossof lluid therefrom; it is con- I venient and -practical-to'butt theedges of the liner plates' without joining orsealing the same.

AThe-corrosive condensate-inA the vapor region oftank 1 may thus reachthe absorbent-insulating material -7-and be absorbed therein. --Liner--Sfunctions -as-v anV expendable anode, as will-be hereinafter-described.-

Liner-S--isJ secured-to tank l-by a pluralityl'of stud's 9 which are-welded to the inner-surface of the tank.

Studs I9 project inwardly through coating-6, insulating material 7,- andextend through suitable-openings in liner 8. --A sleeve-10 cennposedofan insulatingmaterialfis disposed around each stud 9 and theannularflang'e '11 of sleeve- 10 bears against'the outersurface/'ofliner -8.=

Sleeves-10 serve to-maintain studs i9 o`t of contact=with=-"linerI-S-an'd preventelectrical conduction-bymetallie con` t tacttherebetween. --The outer-threadedlendof each stud 9 receives a-Ametalwasher-12 andisengaged by a-'nut 13. A portionofl the lvapor-forming atthe-liquidlevel in tank l-rtends---to penetrate behind lirierfsheetsSand condense on the inner surfacei'of tank 1H and'wet insu-' latingmaterial 7.. This condensed vaporwhich is absorbed' in the insulatingmaterial functions as an electrolyte' and provides; electricalcontactthrough defects in coating between tank surfaces 1 and liner.8.

A sourceof low-voltage current, such as a rectier ,or

generatorlt; may-be employed to apply direct current to the tank landliner 8. A lead lconnects-the generator or other ,source of current to'a.suitableterminal `on the tank- 1.-.

Patented. May 8, 195.6.

A second `lead-16 extends from generatorl .w throughnaninsulatedopening, in tank --1 ,and coating ,6r y. and-.isconnected-to:aterminalfon liner.8.-\ As tank 1i .isf thesurface,which-iis. to be-y cathodically :protected against corrosion, itis made the cathode, and liner 8 is made the anode.

The insulating material 7 and liner 8 is applied to all the tanksurfaces 1 which are apt to be continually or intermittently exposed tothe contained vapor through the defects in coating 6. lf the liquid intank l is to be maintained at a constant level, the insulating materialneed only extend upwardly from a point slightly below the fixed liquidlevel in order to embrace the tank surfaces exposed to the vapor. Inthis case the tank surfaces below theliquid level may be cathodicallyprotected by commonly known means. However, if the liquid level in tankl is apt to fluctuate or if the tank is periodically emptied and filled,the entire internal surface of tank 1 will, at one time or another, beexposed to the vapor and thus should be coated with the insulatingmaterial 7 and liner tl.

A second embodiment of the present invention is shown in Figs. 3 and 4as applied to a tank 17 bearing no protective coating, such as glass orplastic but otherwise corresponding to tank 1 in the previousembodiment.

An absorbent insulating material i8, such as glass fiber` felt or thelike, is applied to the inner surface of tank 17.

An expendable metal liner 19, similar to liner S previously described,is disposed against insulating material 18 and secured to tank 17 by aplurality of studs 26.

Studs 2t) are welded to the inner surface of tank 17 and provideelectrical contact between tank i7 and liner 19. Studs extend inwardlythrough insulating material 1S and through suitable openings in liner19. The outer end of each stud 20 is engaged by a retaining nut 2l or isotherwise secured.

Liner 19 may consist of separate pieces of aluminum, magnesium, zinc orany metal which is anodic to the metal of the tank 17, or liner 19 mayconsist of a number of perforated plates of the aforementioned class ofmetals. The condensed vapor which is absorbed in material 18 functionsas an electrolyte and is capable of conducting an electrical current.Thus the anodic metal liner 19 is corroded by galvanic action and thetank i7 is protected from corrosion until the liner 19 is expended.

To promote corrosion of the expendable liner 19, it may be preferred toinsulate liner 19 from tank i7 instead of providing electrical contacttherebetween through studs 20 and to apply a low voltage current to thesystem, as described in the first embodiment, with the liner being madethe anode and the tank the cathode.

Conversely, in the first embodiment, electrical contact between tank land liner 8 may be provided through uninsulated studs and a dissimilaranodic metal used as the anode to promote corrosion of the expendableliner.

The present invention may be employed to protect metal surfaces from anytype of vapor which will conduct an electric current when condensed,such as water, salts, acids or the like.

The metal surfaces to be protected may include such articles as pierpiles or dredge boats and equipment which are intermittently subjectedto water spray and varying water levels due to tides, or to any type ofmetal tanks, such as petroleum storage tanks which are to be protectedfrom hydrogen sulfide and water vapor.

Various embodiments may be employed within the scope of the followingclaims.

l claim:

l. A cathodically protected metal article, which comprises a firstmetallic member having a surface subject to corrosion when exposed to aliquid capable of conducting an eectric current, a second metallicmember extending substantially coextensively with said first member andin spaced relation thereto and having a plurality of openings therein, aplurality of spaced metal means extending from one member to the othersaid member to support the members in fixed spaced relation and providea clearance between the members into which the openings in the secondmember communicate for passage of said liquid, electrically insulatingabsorbent material confined within the clearance between the members andadapted to absorb said liquid with the absorbed liquid functioning as anelectrolyte to provide an electrical connection between the membersthrough said electrolyte, and means electrically connecting said firstand second members other than said electrolyte to provide a secondelectrical connection between the members and to complete the electriccircuit between said members, the said first member being the cathodeand the second member the anode in said circuit to thereby promotecorrosion of the second member and inhibit corrosion of the firstmember.

2. A cathodically protected storage structure comprising, a metalliccontainer having an inner surface exposed to corrosive condensate in avapor region, a metallic liner disposed within the container andextending generally coextensive with said inner container surface andbeing spaced from said surface to provide` a clearance therebetween,said liner having a series of discontinuities ex tending therethroughand communicating with said clearance, means for attaching said liner inspaced relation to said container, a layer of fibrous absorbentelectrically insulating material confined within said clearance andadapted to absorb condensed vapors with the condensate serving as anelectrolyte therein, and means for electrically connecting said linerand said container to complete an electric circuit through saidcontainer and liner and electrolyte, with said container being disposedas the cathode in the circuit and the said liner the anode in thecircuit to thereby inhibit corrosion of said container and promotecorrosion of said liner.

3. A cathodically protected metal article, which comprises a firstmetallic member having a surface subject to corrosion when exposed to aliquid capable of conducting an electric current, a second metallicmember extending substantially coextensively with said first member andin spaced relation thereto and having a plurality of openings therein, aplurality of spaced metal means extending between each of said membersand secured thereto to support the members in spaced relation andprovide a clearance between the members into which the openings in thesecond member communicate for passage of said liquid, said spaced metalmeans providing an electrical connection between the members, andelectrically insulating absorbent material confined Within the clearancebetween the members and adapted to absorb said liquid with the absorbedliquid functioning as an electrolyte to provide an electrical connectionbetween the members through the electrolyte and to complete theelectrical circuit between the members, the said first member being of ametal cathodic to the second member to thereby promote corrosion of thesecond member and inhibit corrosion of the first member.

4. A cathodically protected metal article, which com- V prises a firstmetallic member having a surface subject to corrosion when exposed to aliquid capable of conducting an electric current, a second metallicmember extending substantially coextensively with said rst member and inspaced relation thereto and having a plurality of openings therein, aplurality of spaced metal means extending between each of said membersto support the members in spaced relation and provide a clearancebetween the members into which the openings in the second membercommunicate for passage of said liquid, electrically insulatingabsorbent material confined within the clearance between the members andadapted to absorb said liquid with the absorbed liquid functioning as anelectrolyte to provide an electrical connection between the membersthrough said electrolyte, means electrically connecting said first andsecond members to complete theelectric circuit between the members andthe electrolyte, and a source of low Voltage current connected to said`connecting means to provide a current to said connecting means with thefirst member being the cathode and the second member the anode in saidcircuit to 5 6 thereby promote corrosion of the second member and2,020,844 Magos et al. NOV. 12, 1935 inhibit corrosion of the rstmember. 2,267,361 Andrus Dec. 23, 1941 2,273,897 Scott Feb. 24, 1942References Cited in the le of this patent 2,485,276 Gerbes Oct. 18, 19495 2,491,225 Stearns Dec. 13, 1949 UNITED STATES PATENTS 1,512,557 MillsOct. 21, 1924

1. A CATHODICALLY PROTECTED METAL ARTICLE, WHICH COMPRISES A FIRSTMETALLIC MEMBER HAVING A SURFACE SUBJECT TO CORROSION WHEN EXPOSED TO ALIQUID CAPABLE OF CONDUCTING AN ELECTRIC CURRENT, A SECOND METALLICMEMBER EXTENDING SUBSTANTIALLY COEXTENSIVELY WITH SAID FIRST MEMBER ANDIN SPACED RELATION THERETO AND HAVING A PLURALITY OF OPENINGS THEREIN, APLURALITY OF SPACED METAL MEANS EXTENDING FROM ONE MEMBER TO THE OTHERSAID MEMBER TO SUPPORT THE MEMBERS IN FIXED SPACED RELATION AND PROVIDEA CLEARANCE BETWEEN THE MEMBERS INTO WHICH THE OPENINGS IN THE SECONDMEMBER COMMUNICATE FOR PASSAGE OF SAID LIQUID, ELECTRICALLY INSULATINGABSORBENT MATERIAL CONFINED WITHIN THE CLEARANCE BETWEEN THE MEMBERS ANDADAPTED TO ABSORB SAID LIQUID WITH THE ABSORBED LIQUID FUNCTIONING AS ANELECTROLYTE TO PROVIDE AN ELECTRICAL CONNECTION BETWEEN THE MEMBERSTHROUGH SAID ELECTROLYTE, AND MEANS ELECTRICALLY CONNECTING SAID FIRSTAND SECOND MEMBERS OTHER THAN SAID ELECTROLYTE TO PROVIDE A SECONDELECTRICAL CONNECTION BETWEEN THE MEMBERS AND TO COMPLETE THE ELECTRICCIRCUIT BETWEEN SAID MEMBERS, THE SAID FIRST MEMBER BEING THE CATHODEAND THE SECOND MEMBER THE ANODE IN SAID CIRCUIT TO THEREBY PROMOTECORROSION OF THE SECOND MEMBER AND INHIBIT CORROSION OF THE FIRSTMEMBER.